(1) Field of the Invention
This invention relates to a hollow multilayer printed wiring board and a process for manufacturing the multilayer printed wiring board. By the term "hollow multilayer printed wiring board" used herein is meant a multilayer printed wiring board which comprises at least two insulating material substrates, on each of which a conductor pattern or patterns are formed, the conductor pattern or patterns being interconnected as may be required, and each of which substrate being spaced apart a predetermined distance from the adjacent substrate or substrates, the space being filled with an insulating gas or liquid.
(2) Description of the Prior Art
The trend toward producing transistors, integrated circuits and other electronic devices and parts of small sizes in recent years has required a substantial increase in the wiring density of multilayer printed wiring boards by reducing the spaces between the parts. For this requirement, substrates having an enhanced dimensional stability must be used. Furthermore the signal conductor patterns must be arranged close to each other, which results in the following defects. First, electrical signals of a signal pattern are transferred to another neighboring signal pattern and interfere with the signals therein or produce noise, that is, the occurrence of so-called crosstalk phenomenon arises. Secondly, the parts, particularly where they are directly bonded to the substrate, cause a temperature rise in the surface of the substrate, thereby influencing the characteristics of the parts and the substrate, and occasionally damaging the parts.
Most conventional multilayer printed wiring boards are prepared by laminating substrates, having formed thereon conductor patterns, by interposing an adhesive layer comprised of glass fibers impregnated with a prepolymer of a thermosetting resin between the substrates. The adhesive layer used, however, must satisfy many requirements, such as good thermal resistance, low shrinkage upon curing and good moldability. With an increase in the packaging density, it becomes more and more difficult to manufacture the composite structure by using the adhesive layer of thermosetting resin-impregnated glass fibers.